The doctrine of mental reservation, or the doctrine of mental equivocation, was a special branch of casuistry developed in the late Middle Ages and the Renaissance, and most often associated with the Jesuits.

Secular use

Mental reservation is a form of deception which is not an outright lie. It was argued for in moral theology, and now in ethics, as a way to fulfill obligations both to tell the truth and to keep secrets from those not entitled to know them (for example, because of the seal of the confessional or other clauses of confidentiality). Mental reservation, however, is regarded as unjustifiable without grave reason for withholding the truth. This condition was necessary to preserve a general idea of truth in social relations.

A wide mental reservation is using equivocations and amphibologies to imply an untruth that is not actually stated. In the strict mental reservation, the speaker mentally adds some qualification to the words which he utters, and the words together with the mental qualification make a true assertion in accordance with fact.

An anecdote often related, for instance by the canonistMartin de Azpilcueta to illustrate his doctrine of a mixed speech (oratoria mixta) combining verbal speech and gestual communication, concerns Francis of Assisi, who allegedly declared to people pursuing a thief that he had just seen, "He hasn't passed by here," at the same time sliding his finger in his sleeve.[1]

Mentalis restrictio in moral theology

The doctrine of mentalis restrictio or mental reservation was most fully enunciated by the 16th-century Spanish theologian Martin de Azpilcueta (often called "Navarrus" because born in the Kingdom of Navarre). Navarrus held that mental reservation involved truths "expressed partly in speech and partly in the mind," relying upon the idea that God hears what is in one's mind while human beings hear only what one speaks. Therefore the Christian's moral duty was to tell the truth to God. Reserving some of that truth from the ears of human hearers was moral if it served a greater good. The user of the doctrine could reply "I know not" aloud to a human interlocutor, and "to tell you" silently to God, and still be telling the truth (stricte mentalis).

The doctrine of mental reservation was intimately linked with the concept of equivocation, which allowed the speaker to employ double meanings of words to tell the literal truth while concealing a deeper meaning. Navarrus did not by any means originate these ideas, but he gave them a far more broad and liberal interpretation than had anyone up to that time. Other Catholic theological thinkers and writers took up the argument in favor of equivocation and mental reservation. Though the concepts remained controversial within the Roman Catholic Church (which never officially endorsed or upheld the doctrines), the Jesuits came to favor these tactics for their obvious advantages.

The linked doctrines of mental reservation and equivocation became notorious in England during the Elizabethan era and the Jacobean era, when Jesuit agents penetrating England to maintain the Catholic cause were captured by the authorities, and used these concepts in their legal defenses. Robert Southwell (c. 1561–1595), a Jesuit priest and agent (also a poet of note) who was arrested in England in 1592, defended the doctrines at his trial, to the predictable resistance of the authorities. (Southwell was convicted, and executed in 1595.) More famous in his own era was Henry Garnet (1555–1606), who wrote a defense of Southwell in 1598; Garnet was captured by the authorities in 1606 due to his involvement in the Gunpowder Plot. He used the same doctrines in his own defense, with the same result as Southwell: Garnet was executed that year.

The Protestants considered these doctrines as mere justifications for lies. Catholic ethicists also voiced objections: the Jansenist "Blaise Pascal...attacked the Jesuits in the seventeenth century for what he saw as their moral laxity."[2] "By 1679, the doctrine of mental reservation had become such a scandal that Pope Innocent XI officially condemned it."[3] Other casuists justifying mental reservation included Thomas Sanchez, who was criticized by Pascal in his Provincial Letters — although Sanchez added various restrictions (it should not be used in ordinary circumstances, when one is interrogated by competent magistrates, when a creed is requested, even for heretics, etc.), which were ignored by Pascal. Of the 26 theses condemned by Pope Innocent XI, several were in Sanchez's works (see op. mor. in præc. Decalogi, III, vi, n. 15). One of them stated:

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If anyone, by himself, or before others, whether under examination or of his own accord, whether for amusement or for any other purpose, should swear that he has not done something which he has really done, having in mind something else which he has not done, or some way of doing it other than the way he employed, or anything else that is true: he does not lie nor perjure himself.

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This type of equivocation was famously mocked in the porter's speech in Shakespeare's Macbeth, in which the porter directly alludes to the practice of deceiving under oath by means of equivocation.

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Faith, here's an equivocator, that could swear in both the scales against either scale; who committed treason enough for God's sake, yet could not equivocate to heaven. (Macbeth, Act 2, Scene 3)

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Following Innocent XI's condemnation of strict mental reservation, equivocation was still considered orthodox, and was revived and defended by Alphonsus Liguori. The Jesuit Gabriel Daniel wrote in 1694 a reply to Pascal's Provincial Letters, titled Entretiens de Cleanthe et d'Eudoxe sur les lettres provinciales, in which he accused Pascal of lying, or even of having himself used mental reservation, by not precising all the restrictions given by Sanchez to the use of this form of deception.

To tell the truth is thus a duty; but it is only in respect to one who has a right to the truth. But no one has a right to a truth which injures others.[4]

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On the other hand, Kant asserted, in the Groundwork of the Metaphysic of Morals, that lying, or deception of any kind, would be forbidden under any interpretation and in any circumstance. In Groundwork, Kant gives the example of a person who seeks to borrow money without intending to pay it back. The maxim of this action, says Kant, results in a contradiction in conceivability (and thus contradicts perfect duty) because it would logically contradict the reliability of language. If it is universally acceptable to lie, then no one would believe anyone and all truths would be assumed to be lies (this last clause was accepted by casuists, hence the reasons for restrictions given to the cases where deception was authorized).[5] The right to deceive could also not be claimed because it would deny the status of the person deceived as an end in himself. And the theft would be incompatible with a possible kingdom of ends. Therefore, Kant denied the right to lie or deceive for any reason, regardless of context or anticipated consequences.

Others

The doctrines have also been criticized by Sissela Bok[6] and by Paul Ekman, who defines lies by omission as the main form of lying — though larger and more complex moral and ethical issues of lying and truth-telling extend far beyond these specific doctrines. Ekman, however, does not consider cases of deception where "it is improper to question" the truth as real form of deceptions[7] — this sort of case, where communication of truth is not to be expected and so deception is justified, was included by casuists.[5]

Social psychologists have advanced cases[8] where the actor is confronted with an avoidance-avoidance conflict, in which he both doesn't want to say the truth and doesn't want to make an outright lie; in such circumstances, equivocal statements are standardly preferred by locutors. This type of equivocation has been defined as “nonstraightforward communication...ambiguous, contradictory, tangential, obscure or even evasive.”[9] People typically equivocate when posed a question to which all of the possible replies have potentially negative consequences, yet a reply is still expected (the situational theory of communicative conflict).[10]

Well, the general teaching about mental reservation is that you are not permitted to tell a lie. On the other hand, you may be put in a position where you have to answer, and there may be circumstances in which you can use an ambiguous expression realising that the person who you are talking to will accept an untrue version of whatever it may be – permitting that to happen, not willing that it happened, that would be lying. It really is a matter of trying to deal with extraordinarily difficult matters that may arise in social relations where people may ask questions that you simply cannot answer. Everybody knows that this kind of thing is liable to happen. So mental reservation is, in a sense, a way of answering without lying.